Interpretive Summary: Iron is an essential nutrient needed for proper plant growth and in human nutrition. In many soil types, iron is unavailable in high enough concentrations to support proper plant growth. In such soils, plants have inadequate levels of iron, and thus suffer from iron-deficiency. Iron- deficiency is a common problem in many of the agricultural areas worldwide, and is especially common in citrus cultivation. The only known effective way to overcome iron-deficiency in citrus cultivation is to select varieties that appear to be more efficient in obtaining sufficient levels of iron from these soils. These varieties are known to be more tolerant to iron-deficiency stress. In this report, a large number of citrus varieties are screened for their tolerances to iron- deficiency stress. These findings allow us to rank these varieties as highly tolerant, moderately tolerant, poorly tolerant, and non-tolerant. It was discovered that many of the highly tolerant varieties are related to lemons and citrons. This finding will greatly facilitate future breeding programs designed towards producing new, highly tolerant citrus varieties, which in turn, will greatly increase citrus cultivation efficiency and fruit quality. This will also decrease the levels of the applications of metal ion nutrients, and thus contribute to better sustained agricultural practices.